[Synthesis and study on the interaction of rare earth complexes of N', N-bis(2-pyridinecarboxamide)-1, 2-ethane with DNA].

Four rare earth complexes of N', N-bis(2-pyridinecarboxamide)-1, 2-ethane were synthesized and characterized by elemental analysis, conductivity measurement, thermal studies, IR and electronic spectra. The composition of the four complexes is Ln(H2L)(NO3)2 x 3H2O (Ln=Sm, Eu, Gd, Tb). Results of spectral measurements indicate that the oxygen of carbonyl and the nitrogen of pyridyl coordinate with Ln(III) respectively, and the NO3- shows bidentate coordination. So the four complexes are 1 : 1 chelated complexes. The interaction between Sm(H2L) (NO3)2 x 3H2O and DNA was studied by employing UV-Visible (UV-Vis) spectra, fluorescence spectra and SERS spectra. Experimental results show that with the incremental addition of DNA, the bands at 265 nm show hypochromism accompanied by a small red shift and the binding constant Kb Obtained is 1.24 x 10(5). Meanwhile fluorescence spectra show that the addition of [Sm(H2L) (NO3)2] (NO3) x 3H2O to DNA pretreated with EB causes an appreciable reduction in fluorescence intensity, indicating that the complex competes with ethidium bromide in binding to DNA, and free ethidium bromide increases. The addition of DNA causes the SERS signals of the complex to weaken and the band at 1 282 cm(-1) to disappear, which suggests that the planar pyridine molecule of the ligand may partly be inserted into the double-stranded helix plane in DNA, making pi electronic density of aromatic rings in complex change. The above phenomena indicate that [Sm(H2L) (NO3)] (NO3) x 3H2O interacts intensively with DNA.